1. Field of the Invention
The present invention relates to an optical medium having a dual layer, and more particularly, to an apparatus and a method of controlling a layer change of an optical medium having a dual layer.
2. Description of the Related Art
Generally, an optical medium is a disc-type recording and reproducing medium. Optical media that are currently available are roughly divided into digital versatile discs (DVDs) and compact discs (CDs). An optical medium having a dual layer has been introduced to satisfy an increasing demand to store more data into an optical medium. Dual layer optical media that are currently available includes a dual layer DVD.
FIG. 1 shows a flowchart illustrating a conventional method of changing a layer in dual layer optical media. That is, where a dual layer optical medium is placed on an optical driver to be driven, and where a layer change of the optical medium is requested, a kick voltage (kick force) Fspk, as shown in FIG. 2, is added to a focus actuator driving signal (focus of drive, FOD) in operation 101. The kick voltage is a kick force which is needed to have a focus point break away from a current layer. Therefore, the focus point begins to break away from the current layer by the FOD, to which the kick voltage is added.
In operation 102, it is monitored whether a level of a generated focus actuator error signal (FE) arrives at a SFok+Fkll level shown in FIG. 2. At this time, the FOD maintains the state in which the kick voltage Fspk is added to the FOD. SFok is a hysteresis level of the FE, and Fkll is the FE level where a break operation of the focus actuator begins. The break operation is an operation to reduce the kick force provided to the focus actuator to pull in the focus point to a target layer.
Where it is determined in the operation 102 that the FE level arrives at the SFok+Fkll level, the monitoring level for the FE level changes to an Fklf level and the FE level is monitored till the FE level arrives at the Fklf level in operation 103. The Fklf level is an FE level corresponding to the end point of a kick interval.
Where it is determined in the operation 103 that the FE level arrives at the Fklf level shown in FIG. 2, the adding of the kick voltage to the FOD stops in operation 104 so as to stop the kick operation. Accordingly, interval t on the FOD shown in FIG. 2 becomes the kick operation interval of the focus actuator.
Where the kick operation interval ends, an FOD having a reference voltage Vref is generated in operation 105. In operation 106, it is monitored whether the FE level arrives at the Fkll level shown in FIG. 2. An interval from a time where the FOD is generated as the reference voltage Vref, to a time where the FE level arrives at the Fkll level, is an inertia interval in which a kick voltage or a brake voltage is not added.
Where it is determined in the operation 106 that the FE level arrives at the Fkll level, an FOD having a brake voltage FkBk is generated in operation 107. Accordingly, the focus actuator begins to perform an operation to reduce the voltage, which arrived at the kick voltage, so as to pull the focus point into a desired layer.
In operation 108, it is monitored whether the FE level arrives at a (3/2) SFok+Fkll level shown in FIG. 2. Where it is determined that the FE level arrives at the (3/2) SFok+Fkll level, the monitoring pointer for the FE level again changes into the SFok+Fkll level in operation 109. Where it is determined in the operation 109 that the FE level arrives at the SFok+Fkll level, the brake operation is processed to stop in operation 110. That is, adding of the brake voltage to the FOD stops. Accordingly, the brake operation interval becomes T′ interval of FIG. 2. Then, the focus actuator performs a focus pulling operation into a corresponding layer in operation 111.
FIG. 3 shows a diagram illustrating a layer change of an optical medium from layer 0 to layer 1. From focus point A, a kick voltage Fspk is added to a FOD for a kick interval (t) so that the focus point of the focus actuator breaks away from the layer 0. Then, during an inertia interval T, only a reference voltage is generated in the FOD. Thereafter, from a focus point B, a brake voltage FkBk is added to the FOD for a brake interval T′ so as to pull a focus point C into the layer 1.
However, since predetermined voltage values are used as the kick voltage and the brake voltage which control the layer change, if a deviation occurs in the FE level and the FE waveform, according to the sensitivity of the focus actuator, the location of a pickup, and the type of the optical medium, or if there is a difference between FE levels generated in an inner circumference and an outer circumference of the optical medium, the focus point cannot be accurately detected. Accordingly, a focus drop occurs and the layer change fails.